1. Field of the Invention
The present invention relates to the reading of bar codes generally and, more particularly, to novel apparatus for reading bar codes, particularly those having variable print/contrast ratios, such as are encountered, for example, on silicon wafers during both the manufacture of the wafers and the manufacture of the integrated circuits on the wafers, during the production of heat treated parts such as turbine blades, during the manufacture of nuclear rods, and during the manufacture of compact disks.
2. Background Art
Conventional means for reading bar codes are generally unsatisfactory for reading bar codes which have variable print/contrast ratios. Such bar codes are encountered, for example on silicon wafers during both the manufacture of the wafers and the manufacture of the integrated circuits on the wafers, on heat treated parts such as turbine blades during their production, on nuclear rods during their manufacture, and on compact disks during their manufacture. The problem with reading such bar codes is that the print/contrast ratios and reflectivity of the bar codes can change greatly as process steps are carried out and can even vary greatly across a given bar code.
While the present invention is described in detail as being applied to the reading of bar codes on silicon wafers, the teaching of the invention can be applied to the reading of a wide range of bar codes, and particularly difficult to read bar codes as indicated by, but not limited to, the above examples.
Integrated circuits have found extensive use in digital data processing equipment and have permitted the size of such equipment to shrink by many orders of magnitude. In the manufacturing process, a number of such circuits are formed on a silicon wafer disk by successive deposition and etching steps, following which the disk is cut into individual circuits, or chips.
The wafers are marked with identifying bar codes which are typically etched into the surfaces of the wafers by the manufacturer of the wafers. It is critical that such bar codes be accurately read as the wafers move through the circuit manufacturing process to ensure that the proper operations are performed and to identify the wafers before being cut. Conventional bar code reading devices used in such equipment provide poor performance, due to changing print/contrast ratios as the wafers move through the manufacturing process and due to the wide ranging reflectivity of the bar codes, the latter resulting from the fact that the bar codes are not printed on the wafers but are laser-etched into the surfaces thereof. If the bar code reader is of the scanning type having an oscillating light beam, there is a changing focal point as the bar code is scanned from end to end. The types of readers that have a detector of constant distance from the wafer require the additional complication that the position of the wafer be changed as attempts are made to read the bar code.
Therefore, it would be desirable to have reliable means by which bar codes can be read during the manufacture of integrated circuits and also as a means of verification in the wafer manufacturing process and in other cases in which bar codes are difficult to read using conventional equipment.
Accordingly, it is a principal object of the present invention to provide means for reading bar codes having variable print/contrast and reflectivities.
It is an additional object of the invention to provide such means that reads the bar codes at a constant focal point.
It is a further object of the invention to provide such means that can be employed to read bar codes on silicon wafers used in the manufacture of integrated circuits both during the manufacture of the circuits and during the manufacture of the wafers.
It is a another object of the invention to provide such means that does not require re-positioning of silicon wafers during the reading of bar codes thereon.
It is yet an additional object of the invention to provide such means that can be retrofitted to existing equipment employed in the wafer and integrated circuit manufacturing processes.
It is yet a further object of the invention to provide such means that provides relatively rapid reading of such bar codes.
Other objects of the present invention, as well as particular features and advantages thereof, will be elucidated in, or be apparent from, the following description and the accompanying drawing figures.